Such an inertization device is known in principle from the prior art. For example, German Patent Specification DE 198 11 851 C2 describes an inertization device for reducing the risk of fire and for extinguishing fires in enclosed spaces. The known system is configured to decrease the oxygen concentration within an enclosed room (hereinafter called “protective room”) to a base inertization level, which can be preset in advance, and in the event of a fire to rapidly further decrease the oxygen concentration to a specific full inertization level, thereby enabling the fire to be effectively extinguished with the smallest possible storage capacity required for inert gas tanks. For this purpose, the known device has an inert gas system that can be controlled via a control unit, and a supply pipe system that is connected to the inert gas system and to the protective room, via which the inert gas provided by the inert gas system is supplied to the protective room. The inert gas system can be either a steel cylinder battery, in which the inert gas is stored in compressed form or a system for generating inert gases.
In general, the functioning method of an inertization device for reducing the risk of fire and for extinguishing fires in enclosed spaces is based upon the knowledge, that in enclosed spaces that are visited only occasionally by humans or animals, and whose equipment reacts sensitively to the effects of water, the risk of fire can be countered by reducing the oxygen concentration in the relevant area in a sustained manner to a level of, for example, approximately 12 vol.-% under normal conditions. At this oxygen concentration, most combustible materials can no longer burn. The main areas of application include especially ADP areas, electrical switching and distribution spaces, enclosed facilities, and storage areas containing high-value commercial goods.
The prevention and/or extinguishing effect that results from the inertization process is based upon the principle of oxygen displacement. As is known, normal environmental air is made up of 21 vol.-% oxygen, 78 vol.-% nitrogen and 1 vol.-% other gases. In order to effectively decrease the risk that a fire will start in a protective room, the nitrogen concentration is further increased in the relevant space by introducing inert gas, such as nitrogen, thereby decreasing the ratio of oxygen. With respect to extinguishing fire, it is known that an extinguishing effect is generated when the oxygen ratio drops below 15 vol.-%. Depending upon the combustible materials that are present inside the protective room, a further decrease in the oxygen ratio, for example to 12 vol.-%, may be necessary. In other words, with a sustained inertization of the protective room to a so-called “base inertization level,” at which the oxygen ratio in the air inside the room is decreased, for example to below 15 vol.-%, the risk of a fire igniting inside the protective room can be effectively decreased.
The term “base inertization level” used herein is generally understood to refer to an oxygen concentration in the air inside the protective room that is reduced as compared with the oxygen concentration of normal environmental air, whereby, however, in principle this reduced oxygen concentration presents no danger of any kind to persons or animals, so that they are still able to enter the protective room with certain protective measures. As was already mentioned, the establishment of a base inertization level, which, in contrast to the so-called “full-inertization level”, need not correspond to an oxygen ratio that is decreased such that fire is effectively extinguished, serves primarily to reduce the risk of a fire igniting within the protective room. The base inertization level corresponds to an oxygen concentration of, for example, 13 vol.-% to 15 vol.-%-depending upon the circumstances of the individual case.
In contrast, the term “full inertization level” refers to an oxygen concentration that is reduced further as compared with the oxygen concentration of the base inertization level, in which the flammability of most materials is already decreased so far, that they are no longer capable of igniting. Depending upon the fire load inside the protective room, the full inertization level generally ranges from 11 vol.-% to 12 vol.-% oxygen concentration.
Although the reduced oxygen concentration which corresponds to the base inertization level in the air inside the protective room presents no danger to persons and animals in principle, so that they can safely enter the protective room, at least for short periods of time, without significant hardships, for example without gas masks, certain nationally stipulated safety measures must be adhered to in entering a room that has been rendered inert in a sustained fashion to a base inertization level, because, in principle, a stay in a reduced oxygen atmosphere can lead to an oxygen deficiency, which under certain circumstances can have physiological consequences in the human organism. These safety measures are prescribed in the respective national regulations, and are dependent especially upon the level of the reduced oxygen concentration that corresponds to the base inertization level.
In the following Table 1, these effects on the human organism and on the combustibility of materials are presented.
In order to fulfill the safety measures with respect to the accessibility of the protected room stipulated in the national regulations, which become more strict as the oxygen ratio in the air inside the protective room decreases, in a simple manner that is especially easy to implement, it would be conceivable for the purpose of and for the duration of passage into the room to raise the sustained inertization of the protective room from the base inertization level to a so-called accessibility level, at which the stipulated safety requirements are lower and can be fulfilled without major inconvenience.
TABLE 1Effect on theOxygen ratio insideEffect on thecombustibilitythe protective roomhuman organismof materials 8 vol.-%Risk to lifeNot combustible10 vol.-%Discernment andNot combustiblesensitivity to paindiminish12 vol.-%Fatigue, elevationDifficult to igniteof respiratoryvolume and pulse15 vol.-%NoneDifficult to ignite21 vol.-%NoneNone
For example, in a protective room that under normal conditions is permanently inertized to a base inertization level of, for example, 13.8 to 14.5 vol.-%, at which, according to Table 1, an effective suppression of fire can be achieved, it would make sense to reduce the oxygen ratio to an accessibility level, for example of 15 to 18 vol.-%, when it is to be entered, for example for maintenance purposes.
From a medical point of view, a temporary stay in an oxygen atmosphere that has been reduced to this accessibility level is safe for persons who have no cardiac, circulatory, vascular or respiratory illnesses, so that the respective national regulations governing this require no, or only minor, additional safety measures.
Ordinarily, raising the inertization level established inside the protective room from the base inertization level to the accessibility level is accomplished via a corresponding control of the inert gas system. In that regard, it is practical, especially for economic reasons, to consistently maintain the inertization level established inside the protective room at the accessibility level during passage into the protective room (for instance with a corresponding control range), in order to minimize the quantity of inert gas to be introduced back into the protective room once the visit has been completed, in order to reestablish the base inertization level. For this reason, the inert gas system should also be generating and/or providing inert gas during the period of passage into the protective room, so that the inert gas will be correspondingly supplied to the protective room in order to maintain the inertization level there at the accessibility level (optionally with a specific control range).
In the process it is noted, that the term “accessibility level” used herein refers to an oxygen concentration in the air inside the protective room which is reduced in comparison with the oxygen concentration of the normal ambient air, at which the respective national guidelines require no, or only minor, supplementary safety measures for passage into the protective room. As a rule, the accessibility level corresponds to an oxygen ratio in the room air that is higher than a base inertization level.
It is known that the inert gas rate to be provided by the inert gas system can be dependent especially upon the inertization level to be established inside the protective room (accessibility level, base inertization level, full inertization level) and the air exchange rate inside the protective room, but also upon other parameters, such as the temperature or the pressure inside the protective room.
Accordingly, it is necessary for the inert gas system installed inside the inertization device to be configured so as to be capable of providing inert gas at any time, so that a preset inertization level can be maintained inside the protective room. In particular, the inert gas system should be capable of providing inert gas at different inert gas rates at any time, based upon the respective requirements, to be able to compensate for leakage from the protective room, possible inert gas losses via air conditioning units and/or ventilation systems inside the protective room or by the removal of goods from the protective room. On the other hand, the inert gas system should be configured in terms of its capacity, such that it is able to provide a sufficient inert gas rate so that a preset inertization level can be restored within a desired time interval.
Ordinarily, a suitable inert gas system for this purpose is one that can be controlled via an inert gas system control unit, whereby the inert gas rate provided by the inert gas system can be correspondingly controlled via the inert gas system control unit.